No. Well, not this week, anyway. Though you'd be forgiven for fretting when you heard the news that the Americans had lost control of one of their spy satellites and that it was expected to head earthwards.

Certainly something the size of a small bus, as the dodgy satellite is reported to be, falling out of the sky could potentially cause a lot of damage - depending on where it falls, of course.

Fears are exacerbated by the fact that anything falling from space into the atmosphere is likely to get extremely hot indeed. So potentially you could have a Hollywood-esque scenario of bits of flaming stuff crashing down on to city streets.

In fact, that's not terribly likely. According to scientists, anything entering the Earth's atmosphere from space would have to be very heat-resistant indeed: it is more likely that debris from the rogue satellite will simply burn up before it gets anywhere near the ground.

Experts also point out that much of the planet's surface is covered with water: as Gordon Jondroe, a White House spokesman, noted earlier this week: "Given that 75% of the Earth is covered with water and much of the land is uninhabited, the likely percentage of this satellite or any debris falling into a populated area is very small."

But even if this satellite isn't likely to bounce on to your head, let's not forget that there is a lot of what's known as space junk out there. While the old adage, what goes up must come down, doesn't necessarily apply to objects outside the effects of gravity, there is nonetheless the possibility that some of this stuff could re-enter the atmosphere and make it to Earth.

Current estimates put the amount of space junk - which ranges from jettisoned bits of spacecraft to nuts and bolts and the liquid components of astronaut waste (which freezes when it's ejected into space) - at something like 1m bits of, well, crap, floating around the planet.

A bigger threat has always been asteroids and meteors; a huge bit of rock from outer space is thought to have done for the dinosaurs, and more recently we had a narrow squeak (in astronomical terms) when a 600ft asteroid zoomed passed us at a distance of just 538,000km.

This isn't the first time that a satellite has returned to Earth in a more disorganised fashion than planned. In 1979, Skylab broke up and fell back to Earth, landing mostly in the Indian Ocean and some very empty bits of Western Australia. In 2001, the 135-tonne Mir just burnt.

But back to the more immediate threat of that duff US spy satellite. It's due to hit the atmosphere towards the end of next month. Nobody quite knows how much hydrazine rocket fuel it might still contain, so if you hear an agitated hen saying "the sky is falling", she might not be joking.